1. Field of the Invention
The present invention relates to a recording medium suitable for use in ink-jet recording and an ink-jet recording process using such a recording medium.
2. Related Background Art
An ink-jet recording system is a recording system in which recording is conducted by generating and ejecting droplets of an ink by one of various ink ejection systems, for example, an electrostatic attraction system, a system using a piezoelectric element to give an ink mechanical vibration or change, or a system in which an ink is heated to form bubbles in the ink, thereby using the pressure thus produced, and applying the whole or a part of the droplets to a recording medium such as paper or a plastic film coated with an ink-receiving layer. The ink-jet recording system attracts attention as a printing method which scarcely produces noise and can conduct high-speed printing and multi-color printing.
As inks used for the ink-jet recording system, inks comprising water as a principal component are mainly used from the viewpoints of safety, printability, etc. Water-soluble organic solvents such as polyhydric alcohols are often added to such inks with a view toward preventing clogging of orifices and improving ejection stability. Therefore, it is required of recording media used in ink-jet recording that images formed thereon by these inks become excellent in water fastness (hereinafter referred to as xe2x80x9cthe ability to improve the water fastness of imagesxe2x80x9d).
Conventionally known recording media for ink-jet recording, which have been proposed for meeting such a requirement, include, for example, a recording sheet described in Japanese Patent Application Laid-Open No. 57-36692, comprising a water-insoluble polymer latex composed of a copolymer with a monomer having a tertiary amino group or quaternary ammonium group, a recording sheet described in Japanese Patent Application Laid-Open No. 58-177390, comprising an electrically-conductive agent of the quaternary ammonium salt type, a recording sheet described in Japanese Patent Application Laid-Open No. 59-20696, comprising a diallyldialkylammonium halide, and a recording sheet described in Japanese Patent Application Laid-Open No. 59-146889, comprising a dicyandiamide-formalin condensate.
Besides, there are described a recording sheet comprising a quaternary cationic or amine compound in Japanese Patent Application Laid-Open No. 61-277484, a recording sheet comprising polyallylamine hydrochloride in Japanese Patent Application Laid-Open No. 62-174184, a recording sheet comprising an organic acid salt of polyethyleneimine in Japanese Patent Application Laid-Open No. 59-198186, a recording sheet comprising a quaternized product of polyethyleneimine in Japanese Patent Application Laid-Open No. 59-198188, a recording sheet comprising a poly(dialkanolallylamine) derivative in Japanese Patent Application Laid-Open No. 63-280681, a recording sheet comprising a polymer based on a (meth)acrylic acid alkyl quaternary ammonium salt or a polymer based on a (meth)acrylamidoalkyl quaternary ammonium salt in Japanese Patent Application Laid-Open No. 63-115780, and a recording medium comprising a polyvinyl acetal resin and a cationic compound as essential components in Japanese Patent Application Laid-Open No. 7-61113.
Furthermore, there is also proposed an additive for ink-jet recording comprising, as an active ingredient, a polymer based on a (meth)acrylic acid alkyl quaternary ammonium salt having a benzyl group or a polymer based on a (meth)acrylamidoalkyl quaternary ammonium salt having a benzyl group in Japanese Patent Application Laid-Open No. 8-108618.
With the improvement in performance of ink-jet recording apparatus, such as speeding up of recording and multi-coloring of images, in recent years, ink-jet recording media have also been required to have higher and wider properties. Particularly, the recording media are strongly required to have the following properties:
(1) being able to stably store an image formed thereon for a long period of time without undergoing changes even when left to stand in a high-temperature and high-humidity environment;
(2) providing a printed image having excellent light fastness;
(3) having high ink absorbency (absorbing capacity being great, and absorbing time being short);
(4) providing dots high in optical density and clear in periphery; and
(5) having an ink-receiving layer excellent in water resistance and providing a printed image excellent in water fastness.
In addition to the above properties, such recording media are required to satisfy the following properties at the same time:
(6) being excellent in adhesion between an ink-receiving layer and a base material;
(7) providing dots having a substantially round shape and a smooth periphery when an ink is applied thereto;
(8) undergoing little changes in properties and no curling even at varied temperatures and humidities when they are in the form of a sheet;
(9) undergoing no blocking; and
(10) being stable without undergoing deterioration even when they are stored in themselves for a long period of time (in particular, in a high-temperature and high-humidity environment).
Besides, recording sheets for OHP, and the like are further required to have excellent transparency in themselves in addition to the above requirements. More specifically, not only a film as a base material but also an ink-receiving layer provided thereon is required to have excellent transparency.
Further, when a white base material such as a white film or resin-coated paper is used, an ink-receiving layer provided thereon is also required to have excellent transparency so as not to impair the whiteness and/or the glossy feeling of the base material itself. With respect to glossiness in particular, it is a matter of course that the glossiness of an unprinted portion of the recording medium be high, and it is also necessary for a printed portion to have high glossiness.
These properties are often in a relation of trade-off. It has hence been impossible to satisfy them at the same time by the conventionally known techniques. Especially, with the advancement of generalization of ink-jet techniques, opportunities of printing, storing and posting at various places are increasing. Therefore, discoloration or bleeding of printed images becomes a serious problem upon exposure to temperature, humidity or sunlight.
In order to make the quality of an image obtained by ink-jet recording comparable to a silver salt photograph, there is a demand for development of a recording medium capable of providing an image with brighter colors. However, there are the following various difficult problems that confront such a requirement. For example, the recording sheets comprising a cationic compound proposed in Japanese Patent Application Laid-Open Nos. 57-36692, 58-177390, 59-20696, 59-146889, 61-277484, 62-174184, 59-198186, 59-198188, 63-280681, 63-115780 and 7-61113, which have been mentioned above as the recording media of the prior art, are recognized to have been markedly enhanced in the ability to improve the water fastness of images compared with any recording sheet without an addition of cationic compound when conducting ink-jet recording thereon. However, the recording sheets containing the cationic compound tend to change the hue of an ink-jet printed portion though it somewhat varies according to the kind of a dye in an ink used, so that the hue of the resultant image becomes greatly different from the hue inherent in the dye, or the image becomes a gloomy image having poor brightness. The reason for it is considered to be due to the fact that since the cationic compound is ionically bonded to the dye having an anionic group to form a great polymeric complex, and the aggregating state of the dye hence undergoes a change, so that the light absorption spectrum inherent in the dye varies.
Further, in recording sheets obtained by providing an ink-receiving layer on a support, such as sheets for OHP, the water fastness of images printed thereon is impaired when left to stand in a high-temperature and high-humidity environment (for example, 30xc2x0 C./80% RH) even if such a cationic compound as proposed in the prior art is used, so that bleeding occurs on the images. Such recording sheets are hence poor in the ability to stably store the image (hereinafter referred to as xe2x80x9cshelf storability of imagexe2x80x9d merely).
With the increase of recording density in ink-jet recording methods in recent years, i.e., increase in shot-in ink quantity, the degree of bleeding of an image when the image is left to stand in a high-temperature and high-humidity environment (for example, 30xc2x0 C./80% RH) comes to be at an unsatisfactory level under the circumstances though it has heretofore been at a fully satisfactory level.
Further, the recording sheets containing the cationic compound proposed in the prior art provide images markedly poor in light fastness compared with recording sheets containing no cationic compound, and so the necessity of improving the light fastness of the resulting image is pointed out.
When a recording medium for ink-jet is prepared by mixing the additive for ink-jet recording proposed in Japanese Patent Application Laid-Open No. 8-108618 with a hydrophilic resin and applying the mixture to a transparent PET film to form an ink-receiving layer, and ink-jet recording is conducted thereon, an image, which is fully satisfactory in coloristic performance and light fastness, is provided. However, bleeding occurs on such an image when the image is left to stand in a high-temperature and high-humidity environment (for example, 30xc2x0 C./80% RH), and so the recording medium is not such that the shelf storability of image can be fully satisfied.
It is accordingly an object of the present invention to provide a recording medium which satisfies the above-described various properties at the same time in a well-balanced relation and is suitable for use in ink-jet recording, and particularly to provide a recording medium which has excellent shelf storability of image in that an image formed thereon undergoes no changes such as bleeding even when it is left to stand for a long period of time under environmental conditions of a high-temperature and a high-humidity after printing, to say nothing of being excellent in the image quality of the image right after printing, and which can provide an image having excellent light fastness though its ink-receiving layer contains a cationic compound, and an ink-jet recording process and an image forming process using such a recording medium.
The above object can be achieved by the present invention described below.
According to the present invention, there is thus provided a recording medium comprising a base material and an ink-receiving layer provided on at least one side of the base material, wherein the ink-receiving layer comprises, as essential components, a hydrophilic resin and a cationic compound having both structural units of the formulae (I) and (II) 
wherein R1, R2, R4 and R5 are independently each other hydrogen or an alkyl group, R3 is a phenyl, naphthyl, benzyl or phenethyl group, R6 is a linear segment comprising a hydrophilic repeating segment and having 10 to 50 carbon atoms, and X is a halide ion, a sulfate ion, an alkylsulfate ion, an alkylsulfonate ion, an arylsulfonate ion, or an acetate ion, and wherein the cationic compound is used in combination with the hydrophilic resin in a proportion of from 1 to 40 parts by weight per 100 parts by weight of the hydrophilic resin.
According to the present invention, there is also provided an ink-jet recording process comprising the step of ejecting ink droplets from an orifice of a recording head to the recording material mentioned above in accordance with a recording signal.